A fine specimen of an ammonite, sawn laterally in two and polished to a fine finish. Both polished interior and natural exterior reveal details of the complex morphology of a fossil cephalopod. This beast may be an example of the Albian ammonite Cleoniceras, or a similar genus. The internal space in the shell is divided into many chambers, which grow larger on the outward spiral, from roughly the size of a rice grain to a human thumb. Ammonite shells were made of aragonite. Some of the chambers in the fossil are infilled by fine silty sediment, while others are vuggy cavities, with an open space between walls lined by calcite crystals.